The present invention relates to a pneumatic tire more particularly to a run flat tire.
In order to maintain safe running when the tire is punctured, various propositions have been made.
FIG. 3 shows typical of such propositions, where the sidewall portion (d) is provided between the carcass (f) and inner liner (i) of airtight rubber with a reinforcing layer (g). This reinforcing layer (g) is made of a vast volume of rubber to support the tire load mainly by itself. Therefore, the ride comfort is sacrificed, and the tire weight is inevitably increased to worsen the fuel consumption, which goes against the times.
FIG. 4 shows another proposition, where two reinforce rubber layers (g1) and (g2) are disposed between three plies (f1, f2 and f3) of the carcass (f) in the sidewall portion (d). In this case, it can be possible to reduce the rubber volume if the target load supporting power is the same level as of FIG. 3. In practice, however, it is difficult to attain a sufficient load supporting power even if the same or more volume of rubber.
Further, even if the sidewall portions are fully reinforced by such reinforcing layers (g, g1, g2) at the sacrifice of the tire weight, ride comfort and the like, it is very difficult to improve run flat performance especially to increase the runable distance, because the tire shoulder portions or buttress portions, which are usually a weakest portion of the tire, contact with the ground at high ground pressure and rapidly fatigued and worn and thus easily broken.